As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased as an energy source for the mobile devices. Among such secondary batteries is a lithium secondary battery having high energy density and high discharge voltage, into which much research has been carried out and which is now commercially and widely used.
Depending upon the shape of a battery case, a secondary battery may be classified as a cylindrical battery having an electrode assembly mounted in a cylindrical metal container, a prismatic battery having an electrode assembly mounted in a prismatic metal container, or a pouch-shaped battery having an electrode assembly mounted in a pouch-shaped case formed of an aluminum laminate sheet.
Also, the electrode assembly mounted in the battery case is a power generating element, having a cathode/separator/anode stack structure, which can be charged and discharged. The electrode assembly may be classified as a jelly roll type electrode assembly configured to have a structure in which a long sheet type cathode and a long sheet type anode, to which active materials are applied, are wound in a state in which a separator is disposed between the cathode and the anode, a stacked type electrode assembly configured to have a structure in which a plurality of cathodes having a predetermined size and a plurality of anodes having a predetermined size are sequentially stacked in a state in which separators are disposed respectively between the cathodes and the anodes, or a stacked/folded type electrode assembly configured to have a structure in which a predetermined number of cathodes and a predetermined number of anodes are sequentially stacked in a state in which separators are disposed respectively between the cathodes and the anodes to constitute a unit cell, such as a bi-cell or a full cell, and then unit cells are wound using a separation film. The jelly roll type electrode assembly has advantages in that the jelly roll type electrode assembly is easy to manufacture and has high energy density per unit mass.
Generally, a jelly roll type electrode assembly is mounted into a cylindrical metal case to manufacture a cylindrical battery.
When a battery is manufactured using such a jelly roll type electrode assembly (hereinafter, simply referred to as a ‘jelly roll’), a cathode/separator/anode stack is wound in a circle, the outermost end of the stack is fixed using a seal tape made of polypropylene (PP) so as to maintain the form of the jelly roll, the stack is mounted in a battery case, i.e. a metal container, an electrolyte is injected into the battery case, and a top cap having an electrode terminal (for example, a cathode terminal) is coupled to an open upper end of the battery case. In this way, a battery is manufactured.
When the secondary battery having the above-described structure comes to the ground or external impact is applied to the secondary battery, however, the jelly roll moves up and down, and therefore, the upper part or the lower part of the jell roll is pressed with the result that the sheets of the jelly roll are deformed, and a short circuit may occur.
Also, the jelly roll is repeatedly expanded and contracted as the secondary battery is repeatedly charged and discharged. At this time, the outer region of the jelly roll is greatly affected by such expansion and contraction. As a result, the electrodes may be broken.
Consequently, the necessity of a technology for fundamentally solving the above-mentioned problem is very high.